DESCRIPTION (provide by applicant): The mosquito is an obligatory vector for the transmission of malaria, a disease that kills about 2 million people every year. The urgency for developing new control strategies is underscored by the development of resistance by parasites to previously effective drugs, by the resistance of mosquitoes to a variety of insecticides, and by the lack of an effective vaccine. Inhibition of the parasite's life cycle in the mosquito is a strategy that needs to be explored. This proposal focuses on the molecular interactions between Plasmodium, the causative agent of malaria, and the mosquito vector. To complete its life cycle in the mosquito, Plasmodium must invade and traverse two different epithelia: the midgut and the salivary gland. A major objective of this proposal is to gain insights on the mechanisms utilized by Plasmodium to traverse these epithelia. Extensive use will be made of phage display libraries, which consist of large numbers of bacteriophages each displaying on their surface a different peptide or protein domain. By incubating the mosquito epithelia with a high-titer stock of the library, phages can be selected that bind with high affinity to surface ligands. Initial results suggest that at least one phage that has been selected by this approach displays a peptide that inhibits Plasmodium invasion of the salivary gland. A transgenic mosquito line that secretes this peptide into the hemolymph will be produced. These genetically modified mosquitoes are expected to be impaired in their ability to transmit the parasite to a vertebrate host. Mosquito salivary gland and midgut surface ligands that are recognized by the selected phages will be isolated and characterized. A phage library that displays Plasmodium proteins will be used to screen for parasite proteins that interact with the mosquito epithelia. A phage display library will be used to investigate the basis for resistance of a selected An. stephensi strain to transmit Plasmodium falciparum. Techniques for the genetic transformation of Ae. aegypti and An. stephensi are already available and transformation of An. gambiae is likely to become available in the near future. A better understanding of how Plasmodium develops in the mosquito may lead to novel strategies for malaria control.